DE4325996A1 (FIGS. 1, 2 and 3) discloses one of headrest height adjusting apparatuses that have been conventionally known. The headrest height adjusting apparatus includes: a basal member secured to a seatback; and a movable member connected to a headrest via stays. The basal member is firmly attached to the seatback by attachment hooks and supports a motor, which serves as a driving member, speed reduction gears and an output gear. The movable member is lifted up and down being guided by guiding portions of the basal member when driving force of the driving member is transmitted to the movable member, i.e., when rotational movement of the output gear (pinion) is transmitted to a rack integrally formed at the movable member. As a result, the headrest is lifted up and down as one unit with the movable member. Further, the headrest height adjusting apparatus has been reduced in weight since the basal member and the movable member are resin moldings.
Meanwhile, because the basal member and the movable member, which are main components of the headrest height adjusting apparatus, are made of resin, these two components are brittle or fragile especially for an impact. For example, when the apparatus bears an excessive impact in an up-and-down direction, for example in an event of a vehicle collision, the basal member or the movable member may be damaged and may not support the headrest any more.
Recent assessment trends have led to further dynamic requirement upgrades than before. In such circumstances, those headrest height adjusting apparatuses with the aforementioned conventional structure may not satisfy the dynamic requirements.
The present invention has been made in view of the above circumstances, and provides a headrest height adjusting apparatus that maintains the headrest appropriately against an impact and can be reduced in weight.